Recently, the advancement of technology has enabled airtightness of spaces such as car interiors of which airtightness had not been able to be successfully achieved. In the case where many passengers stay in a car of which airtightness is high for long hours, external air must be introduced moderately into the interior to prevent the passengers from feeling headache or discomfort resulting from decreased oxygen concentration and increased carbon dioxide concentration.
Direct introduction of external air into the car interior raise health concerns to the passengers due to contaminants such as dust of urban roads and main roads. Thus, a filter may be used that removes the contaminants such as the suspended materials at an inlet of external air.
Conventionally, nonwoven cloth and mechanical filters have been used for the filter. In Patent Literature 1, an overall ventilation system for a car is proposed. No admission is made that the references discussed herein constitute prior art.    Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2004-203367.
Conventional filters such as nonwoven cloth and mechanical filters may not remove suspended material in the air having a diameter not greater than 10 μm (hereinafter referred to as SPM) and especially a diameter not greater than 100 nm (hereinafter referred to as nSPM). When a gas permselective membrane made of polymer material, which can remove SPM and nSPM, is applied to the filter, the sufficient introduction of external air is not attained due to its low gas permeability.
Removal of suspended material in the air such as SPM and nSPM is one of the significant concerns in this art.